The pair had a brief, lighthearted exchange as Nadal helped the journalist build his defence case.
"You were closing your eyes to be more focused on what I am saying," Nadal said.
Tennis coach and ESPN analyst Brad Gilbert said on Twitter it was "so next level funny".
Nadal was in good spirits on his return to the biggest stage since August, after abdominal problems and ankle surgery ended his season early last year.
The Spainard also pulled out of a warm-up tournament in Brisbane last week with a minor thigh strain.
In his on-court interview after his straight-sets victory, Nadal said returning after being out for so long wasn't easy.
"It's not easy to come back after a lot of months, and especially against a player who's super aggressive.
"I'm very, very happy to be through."